1. Field of the Invention
The present invention relates to a radiographic image reading apparatus for reading radiographic image information stored in a storage phosphor sheet.
2. Description of Related Art
A radiographic image reading apparatus outputting image information as digital data has been frequently used for digitizing radiographic image information generated at hospitals to store and to telephotograph the digitized radiographic image information. As a radiographic image reading apparatus for outputting such digital data, a radiographic image reading apparatus using a storage phosphor sheet is well known.
The storage phosphor sheet detects a part of radiation energy which has been transmitted through a subject. At the same time, the storage phosphor sheet can store detected radiation energy in the inside of the storage phosphor sheet. Moreover, the radiation energy stored in the storage phosphor sheet can be taken out as photo-stimulable luminescence by being excited by a laser beam having a predetermined wavelength. The photo-stimulable luminescence from the storage phosphor can be taken out as an electric signal by means of a photoelectric conversion element such as a photomultiplier and the like.
Generally, a storage phosphor sheet can be used in the state in which the storage phosphor sheet is housed in a thin type box-like portable housing called as a cassette. Because a user can easily carry the storage phosphor sheet together with the cassette in such a using form, radiation photographing can be performed by handling the cassette similarly to the cassette of the conventionally used screen film system.
As the handling method of the storage phosphor sheet, as disclosed in Japanese Patent Laid-Open Publication No. Hei 1-237636 specification, a contact carrier system is well known. In the contact carrier system, a flexible storage phosphor sheet is taken out from a cassette with a sucking disk or the like to convey the taken storage phosphor sheet while being nipped with rollers.
Moreover, as disclosed in Japanese Patent Laid-Open Publication No. Hei 11-160821 specification, a noncontact conveyance system has been also proposed. In the noncontact conveyance system, a storage phosphor sheet is stuck to a rigid plate member, and the storage phosphor sheet and the plate member are conveyed by a method contacting with only the plate member (without contacting with the storage phosphor sheet).
Moreover, as shown in an embodiment of the present invention, another noncontact conveyance system can be also considerable. In the noncontact conveyance system, a storage phosphor sheet is attracted to the back plate side of a cassette in advance, and the front plate and the back plate are separated after the taking of the cassette into the inner part of an apparatus to convey the storage phosphor sheet together with the back plate.
As described above, for reading a radiographic image information from a storage phosphor sheet, it is necessary to convey the storage phosphor sheet, a cassette holding the storage phosphor sheet, or a part of the cassette holding the storage phosphor sheet. However, there is the case where an apparatus is obliged to be stopped owing to the occurrence of the situation in which conveyance cannot be continued (conveyance failure) owing to, for example, a jam during the conveyance of the storage phosphor sheet, the cassette holding the storage phosphor sheet, or the part of the cassette holding the storage phosphor sheet.
In case of an apparatus to be used in a medical spot, when the apparatus has stopped owing to the conveyance failure, it is desired not only to inform a user of the occurrence of the conveyance failure, but also to eliminate the conveyance failure immediately, and to restore the apparatus to be able to be used again. The reason is that, if the apparatus is staying to stop, not only emergent diagnostic imaging of a patient cannot be performed, but also it becomes impossible to continue the succeeding medical treatments.
However, the restoring work from such a conveyance failure of the prior art radiographic image reading apparatus using a storage phosphor has been limited to the work of a service man. Consequently, when the conveyance failure occurs, the user is obliged to call a service man and to stop the radiation photographing service until the service man arrives.
In a copy machine, a printer or the like, it has become common knowledge to install a user maintenance mechanism for enabling a user to release a jam when output paper causes the jam. However, such a user maintenance mechanism is not realized in the radiographic image reading apparatus using a storage phosphor. As the reason, the following causes can be considered.
1) In case of the copy machine or a printer, because output paper are very cheap, the presupposition that the output paper which has caused a jam may be in the state of being impossible to use owing to being torn or injured (may be output again) can be concluded. However, in case of the radiographic image reading apparatus using a storage phosphor, a storage phosphor sheet is very expensive. Consequently, the state in which the storage phosphor sheet cannot be used owing to being torn or injured is not allowed. Because of such a restriction, the construction of the mechanism of the user maintenance is difficult.
2) In a copy machine or a printer, even when the output paper which has caused a jam is spoilt, a copy or a print out can be performed again. On the contrary, the storage phosphor sheet used for a radiographic image reading apparatus stores image information of a patient. When the storage phosphor sheet is spoilt, it is necessary to perform re-photographing of the patient. However, the re-photographing makes the patient be exposed by superfluous radiation, which is very undesirable.